It has long been known that internal combustion engines must be provided during their warmup phase with a richer mixture than they require directly after they have attained a predetermined operating temperature. This enrichment is necessary in order to compensate for condensation losses on the inner walls of the intake tube and the cylinders, which are still cold at the time of warmup.
As a rule, this warmup enrichment is selected to be accomplished in accordance with both temperaure and rpm. This provision does permit the attainment of satisfactory smoothness in driving; however, the enrichment is not sufficiently sensitive enough for desired clean exhaust to be attained as well. In the known systems, this has been the result of a demand for a wide safety margin, with the priority being placed on good driving smoothness.